Method for obtaining information about an occupying item in a compartment in a vehicle includes obtaining a series of images of the compartment, each image being taken at a different time and at least one of which includes the occupying item, comparing a later obtained image from the series of images to at least one previously obtained image from the series of images to ascertain the presence of differences between the images, and analyzing the differences to obtain information about the occupying item. One way to compare images is to subtract the later obtained image from the previously obtained image to determine which image pixels have changed in value and analyze the changed pixels. This analysis may involve analyzing a leading edge of the changed pixels and/or analyzing a width of a field of the changed pixels.